linux-kernel - [PATCH] seccomp: rework define for SECCOMP_USER_NOTIF_FLAG

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Date:   Thu, 24 Oct 2019 23:25:39 +0200
From:   Christian Brauner <christian.brauner@...ntu.com>
To:     linux-kernel@...r.kernel.org, keescook@...omium.org
Cc:     luto@...capital.net,
        Christian Brauner <christian.brauner@...ntu.com>
Subject: [PATCH] seccomp: rework define for SECCOMP_USER_NOTIF_FLAG_CONTINUE

Switch from BIT(0) to (1UL << 0).
First, there are already two different forms used in the header, so there's
no need to add a third. Second, the BIT() macros is kernel internal and
afaict not actually exposed to userspace. Maybe there's some magic there
I'm missing but it definitely causes issues when compiling a program that
tries to use SECCOMP_USER_NOTIF_FLAG_CONTINUE. It currently fails in the
following way:

	# github.com/lxc/lxd/lxd
	/usr/bin/ld: $WORK/b001/_x003.o: in function
	`__do_user_notification_continue':
	lxd/main_checkfeature.go:240: undefined reference to `BIT'
	collect2: error: ld returned 1 exit status

Switching to (1UL << 0) should prevent that and is more in line what is
already done in the rest of the header.

Cc: Kees Cook <keescook@...omium.org>
Cc: Andy Lutomirski <luto@...capital.net>
Signed-off-by: Christian Brauner <christian.brauner@...ntu.com>
---
 include/uapi/linux/seccomp.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/uapi/linux/seccomp.h b/include/uapi/linux/seccomp.h
index 61fbbb7c1ee9..9099972200cd 100644
--- a/include/uapi/linux/seccomp.h
+++ b/include/uapi/linux/seccomp.h
@@ -102,7 +102,7 @@ struct seccomp_notif {
  * SECCOMP_USER_NOTIF_FLAG_CONTINUE. Note that SECCOMP_RET_USER_NOTIF can
  * equally be overriden by SECCOMP_USER_NOTIF_FLAG_CONTINUE.
  */
-#define SECCOMP_USER_NOTIF_FLAG_CONTINUE BIT(0)
+#define SECCOMP_USER_NOTIF_FLAG_CONTINUE (1UL << 0)
 
 struct seccomp_notif_resp {
 	__u64 id;
-- 
2.23.0